Patent GB-783625-A (GB)
Title: Improvements in the isolation of difficultly volatile dialkyl esters of dicarboxylicacids from solutions by evaporating the solvent
IPC: C07D213/78
Filed: 1954-12-24
Abstract: <PICT:0783625/III/1> Dialkyl esters of dicarboxylic acids, such as dimethyl terephthalate, are isolated from esterification mixtures containing the ester together with the corresponding alcohol, water and a volatile catalyst (HCl, BF3) by causing the liquid-mixture to flow in the form of a continuously moving film over a surface which is heated to such an extent that the alcohol, water and catalyst are rapidly evaporated and the ester flows off the surface in the fused state.  No saponification occurs during the evaporation, so that the ester is obtained practically free from acid and semi-ester.  The evaporator is preferably maintained under reduced pressure.  A solution of dimethyl terephthalate in methanol containing water (2 per cent) and hydrogen chloride (2 per cent) is fed continuously from tank 1 onto a rotating plate 5 in evaporator 2, which is maintained under a pressure of 15 to 200 mm. Hg absolute.  The solution is thrown off the plate on to the wall of the evaporator which is heated by a steam-jacket to about 165 DEG  C.  Vapours of methanol, water and HCl leave the top of the evaporator, and are passed to a condenser 3; the condensate being collected in receiver 4.  Molten ester runs down the wall of the evaporator and collects in the base, from which it is withdrawn continuously or periodically.  The dimethyl, diethyl and dipropyl esters of isophthalic acid, terephthalic acid and isocinchomeronic acid, are referred to. Specifications 175,077, 288,775, [both in Class 32], and 618,926 are referred to.ALSO:Dialkyl esters of dicarboxylic acids, such as dimethyl terephthalate, are isolated from esterification mixtures containing the ester together with the corresponding alcohol, water and a volatile catalyst (HCl, BF3) by causing the liquid-mixture to flow in the form of a continuously-moving <PICT:0783625/IV (a)/1> film over a surface which is heated to such an extent that the alcohol, water and catalyst are rapidly evaporated and the ester flows off the surface in the fused state.  No saponification occurs during the evaporation, so that the ester is obtained practically free from acid and semi-ester.  The evaporator is preferably maintained under reduced pressure.  A solution of dimethyl terephthalate in methanol containing water (2 per cent) and hydrogen chloride (2 per cent) is fed continuously from tank 1 on to a rotating plate 5 in evaporator 2, which is maintained under a pressure of 15 to 200 mm. Hg. absolute.  The solution is thrown off the plate on to the wall of the evaporator which is heated by a steam-jacket to about 165 DEG  C.  Vapours of methanol, water and HCl leave the top of the evaporator, and are passed to condenser 3; the condensate being collected in receiver 4.  Molten ester runs down the wall of the evaporator and collects in the base, from which it is withdrawn continuously or periodically. The dimethyl, diethyl and dipropyl esters of isophthalic acid, terephthalic acid and isocinchomeronic acid are referred to. Specifications 175,077, 288,775, [both in Class 32], and 618,926, [Group III], are referred to.